1. Field of the Invention
This invention relates to an electronic part unit or assembly constructed from a plurality of electronic parts mounted on a unit circuit board and a process of manufacturing the same.
2. Description of the Related Art
In such apparatus as electronic computers, a structure wherein electronic part units each constructed from a plurality of electronic parts such as LSIs (bare chips) mounted on a unit circuit board are mounted on a printed circuit board or a like board together with other electronic parts or like parts is employed. Such electronic part units are required to be improved in heat radiation and airtightness.
FIG. 1 is a sectional view showing the construction of a prior art. Referring to FIG. 1, reference numeral 1 denotes a unit circuit board formed from ceramics or a like material. A resin wiring layer 2 made of polyimide or a like material and having a wiring pattern is formed on the front surface of the unit circuit board 1. A plurality of IO pins 3 are provided in an array on the rear surface of the unit circuit board 1 and electrically connected suitably to the wiring pattern. Reference numeral 4 denotes a bare chip part such as an LSI. The bare chip parts 4 are mounted on the wiring layer 2 by connecting them to the wiring pattern of the wiring layer 2 by means of solder bumps 5. The bare chips 4 are covered in an airtight enclosed condition with a resin enclosure member 6 made of an epoxy resin material or a silicon resin material (potting agent).
The prior art, however, is disadvantageous in that, since electronic parts are entirely covered with a resin material which cannot, due to its high heat resistance, radiate heat generated from such electronic parts mounted on a unit circuit board, a malfunction or a damage to the circuitry is often caused by the heat. Also there is another disadvantage in that, since an outer periphery of a resin wiring layer is exposed to the external air, water or some other foreign substance likely enters the resin wiring layer and causes a trouble such as deterioration of the insulation.